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.TH XARGS 1 "September 13, 2018"
.SH NAME
xargs \- construct argument lists and invoke utility
.SH SYNOPSIS
.LP
.nf
\fBxargs\fR [\fB-t\fR] [\fB-0\fR] [\fB-p\fR] [\fB-e\fR[\fIeofstr\fR]] [\fB-E\fR \fIeofstr\fR]
     [\fB-I\fR \fIreplstr\fR] [\fB-i\fR[\fIreplstr\fR]] [\fB-L\fR \fInumber\fR] [\fB-l\fR[\fInumber\fR]]
     [\fB-n\fR \fInumber\fR [\fB-x\fR]] [\fB-P\fR \fImaxprocs\fR] [\fB-s\fR \fIsize\fR]
     [\fIutility\fR [\fIargument\fR...]]
.fi

.SH DESCRIPTION
.LP
The \fBxargs\fR utility constructs a command line consisting of the
\fIutility\fR and \fIargument\fR operands specified followed by as many
arguments read in sequence from standard input as fit in length and number
constraints specified by the options. The \fBxargs\fR utility then invokes the
constructed command line and waits for its completion. This sequence is
repeated until an end-of-file condition is detected on standard input or an
invocation of a constructed command line returns an exit status of \fB255\fR.
.sp
.LP
Arguments in the standard input must be separated by unquoted blank characters,
or unescaped blank characters or newline characters. A string of zero or more
non-double-quote (\fB"\fR) and non-newline characters can be quoted by
enclosing them in double-quotes. A string of zero or more non-apostrophe
(\fB\&'\fR) and non-newline characters can be quoted by enclosing them in
apostrophes. Any unquoted character can be escaped by preceding it with a
backslash (\fB\e\fR). The \fIutility\fR are executed one or more times until
the end-of-file is reached. The results are unspecified if the utility named by
\fIutility\fR attempts to read from its standard input.
.sp
.LP
The generated command line length is the sum of the size in bytes of the
utility name and each argument treated as strings, including a null byte
terminator for each of these strings. The \fBxargs\fR utility limits the
command line length such that when the command line is invoked, the combined
argument and environment lists can not exceed \fB{ARG_MAX}\(mi2048\fR bytes.
Within this constraint, if neither the \fB-n\fR nor the \fB-s\fR option is
specified, the default command line length is at least \fB{LINE_MAX}\fR.
.SH OPTIONS
.LP
The following options are supported:
.sp
.ne 2
.na
\fB\fB\fR\fB-e\fR\fB[\fR\fIeofstr\fR\fB]\fR\fR
.ad
.RS 15n
Uses \fIeofstr\fR as the logical end-of-file string. Underscore (\fB_\fR) is
assumed for the logical \fBEOF\fR string if neither \fB-e\fR nor \fB-E\fR is
used. When the \fIeofstr\fR option-argument is omitted, the logical \fBEOF\fR
string capability is disabled and underscores are taken literally. The
\fBxargs\fR utility reads standard input until either end-of-file or the
logical \fBEOF\fR string is encountered.
.RE

.sp
.ne 2
.na
\fB\fB-E\fR \fIeofstr\fR\fR
.ad
.RS 15n
Specifies a logical end-of-file string to replace the default underscore.
\fBxargs\fR reads standard input until either end-of-file or the logical EOF
string is encountered. When \fIeofstr\fR is a null string, the logical
end-of-file string capability is disabled and underscore characters are taken
literally.
.RE

.sp
.ne 2
.na
\fB\fB-I\fR \fIreplstr\fR\fR
.ad
.RS 15n
Insert mode. \fIutility\fR is executed for each line from standard input,
taking the entire line as a single argument, inserting it in \fIargument\fR
\fIs\fR for each occurrence of \fIreplstr\fR. A maximum of five arguments in
\fIargument\fRs can each contain one or more instances of \fIreplstr\fR. Any
blank characters at the beginning of each line are ignored. Constructed
arguments cannot grow larger than 255 bytes. Option \fB-x\fR is forced on. The
\fB-I\fR and \fB-i\fR options are mutually exclusive; the last one specified
takes effect.
.RE

.sp
.ne 2
.na
\fB\fB\fR\fB-i\fR\fB[\fR\fIreplstr\fR\fB]\fR\fR
.ad
.RS 15n
This option is equivalent to \fB-I\fR \fIreplstr\fR. The string \fB{\|}\fR is
assumed for \fIreplstr\fR if the option-argument is omitted.
.RE

.sp
.ne 2
.na
\fB\fB-L\fR \fInumber\fR\fR
.ad
.RS 15n
The \fIutility\fR is executed for each non-empty \fInumber\fR lines of
arguments from standard input. The last invocation of \fIutility\fR is with
fewer lines of arguments if fewer than \fInumber\fR remain. A line is
considered to end with the first newline character unless the last character of
the line is a blank character; a trailing blank character signals continuation
to the next non-empty line, inclusive. The \fB-L\fR, \fB-l\fR, and \fB-n\fR
options are mutually exclusive; the last one specified takes effect.
.RE

.sp
.ne 2
.na
\fB\fB-l[\fR\fInumber\fR\fB]\fR\fR
.ad
.RS 15n
(The letter ell.) This option is equivalent to \fB-L\fR \fInumber\fR. If
\fInumber\fR is omitted, \fB1\fR is assumed. Option \fB-x\fR is forced on.
.RE

.sp
.ne 2
.na
\fB\fB-n\fR \fInumber\fR\fR
.ad
.RS 15n
Invokes \fIutility\fR using as many standard input arguments as possible, up to
\fInumber\fR (a positive decimal integer) arguments maximum. Fewer arguments
are used if:
.RS +4
.TP
.ie t \(bu
.el o
The command line length accumulated exceeds the size specified by the \fB-s\fR
option (or \fB{LINE_MAX}\fR if there is no \fB-s\fR option), or
.RE
.RS +4
.TP
.ie t \(bu
.el o
The last iteration has fewer than \fInumber\fR, but not zero, operands
remaining.
.RE
.RE

.sp
.ne 2
.na
\fB-p\fR
.ad
.RS 15n
Prompt mode. The user is asked whether to execute \fIutility\fR at each
invocation. Trace mode (\fB-t\fR) is turned on to write the command instance to
be executed, followed by a prompt to standard error. An affirmative response
(specific to the user's locale) read from \fB/dev/tty\fR executes the command;
otherwise, that particular invocation of \fIutility\fR is skipped.
.RE

.sp
.ne 2
.na
\fB\fB-P\fR \fImaxprocs\fR\fR
.ad
.RS 15n
Invokes \fIutility\fR using at most \fImaxprocs\fR (a positive decimal integer)
parallel child processes. If \fImaxprocs\fR is zero, then the system
will set a large upper bound to try and run as many processes as
possible.
.RE

.sp
.ne 2
.na
\fB\fB-s\fR \fIsize\fR\fR
.ad
.RS 15n
Invokes \fIutility\fR using as many standard input arguments as possible
yielding a command line length less than \fIsize\fR (a positive decimal
integer) bytes. Fewer arguments are used if:
.RS +4
.TP
.ie t \(bu
.el o
The total number of arguments exceeds that specified by the \fB-n\fR option, or
.RE
.RS +4
.TP
.ie t \(bu
.el o
The total number of lines exceeds that specified by the \fB-L\fR option, or
.RE
.RS +4
.TP
.ie t \(bu
.el o
End of file is encountered on standard input before \fIsize\fR bytes are
accumulated.
.RE
Values of \fIsize\fR up to at least \fB{LINE_MAX}\fR bytes are supported,
provided that the constraints specified in DESCRIPTION are met. It is not
considered an error if a value larger than that supported by the implementation
or exceeding the constraints specified in DESCRIPTION is specified. \fBxargs\fR
uses the largest value it supports within the constraints.
.RE

.sp
.ne 2
.na
\fB\fB-t\fR\fR
.ad
.RS 6n
Enables trace mode. Each generated command line is written to standard error
just prior to invocation.
.RE

.sp
.ne 2
.na
\fB\fB-x\fR\fR
.ad
.RS 6n
Terminates if a command line containing \fInumber\fR arguments (see the
\fB-n\fR option above) or \fInumber\fR lines (see the \fB-L\fR option above)
does not fit in the implied or specified size (see the \fB-s\fR option above).
.RE

.sp
.ne 2
.na
\fB-0\fR
.ad
.RS 6n
Null separator mode.  Instead of using white space or new lines to
delimit arguments, zero bytes are used.  This is suitable for use with
the -print0 argument to \fBfind\fR(1).
.RE

.SH OPERANDS
.LP
The following operands are supported:
.sp
.ne 2
.na
\fB\fIutility\fR\fR
.ad
.RS 12n
The name of the utility to be invoked, found by search path using the
\fBPATH\fR environment variable. (ee \fBenviron\fR(7).) If \fIutility\fR is
omitted, the default is the \fBecho\fR(1) utility. If the \fIutility\fR operand
names any of the special built-in utilities in \fBshell_builtins\fR(1), the
results are undefined.
.RE

.sp
.ne 2
.na
\fB\fIargument\fR\fR
.ad
.RS 12n
An initial option or operand for the invocation of \fIutility\fR.
.RE

.SH USAGE
.LP
The \fB255\fR exit status allows a utility being used by \fBxargs\fR to tell
\fBxargs\fR to terminate if it knows no further invocations using the current
data stream succeeds. Thus, \fIutility\fR should explicitly \fBexit\fR with an
appropriate value to avoid accidentally returning with \fB255\fR.
.sp
.LP
Notice that input is parsed as lines. Blank characters separate arguments. If
\fBxargs\fR is used to bundle output of commands like \fBfind\fR \fIdir\fR
\fB-print\fR or \fBls\fR into commands to be executed, unexpected results are
likely if any filenames contain any blank characters or newline characters.
This can be fixed by using \fBfind\fR to call a script that converts each file
found into a quoted string that is then piped to \fBxargs\fR. Notice that the
quoting rules used by \fBxargs\fR are not the same as in the shell. They were
not made consistent here because existing applications depend on the current
rules and the shell syntax is not fully compatible with it. An easy rule that
can be used to transform any string into a quoted form that \fBxargs\fR
interprets correctly is to precede each character in the string with a
backslash (\fB\e\fR).
.sp
.LP
On implementations with a large value for \fB{ARG_MAX}\fR, \fBxargs\fR can
produce command lines longer than \fB{LINE_MAX}\fR. For invocation of
utilities, this is not a problem. If \fBxargs\fR is being used to create a text
file, users should explicitly set the maximum command line length with the
\fB-s\fR option.
.sp
.LP
The \fBxargs\fR utility returns exit status \fB127\fR if an error occurs so
that applications can distinguish "failure to find a utility" from "invoked
utility exited with an error indication." The value \fB127\fR was chosen
because it is not commonly used for other meanings; most utilities use small
values for "normal error conditions" and the values above \fB128\fR can be
confused with termination due to receipt of a signal. The value \fB126\fR was
chosen in a similar manner to indicate that the utility could be found, but not
invoked.
.SH EXAMPLES
.LP
\fBExample 1 \fRUsing the xargs command
.sp
.LP
The following example moves all files from directory \fB$1\fR to directory
\fB$2\fR, and echo each move command just before doing it:

.sp
.in +2
.nf
example% \fBls $1 | xargs -I {} -t mv $1/{} $2/{}\fR
.fi
.in -2
.sp

.sp
.LP
The following command combines the output of the parenthesised commands onto
one line, which is then written to the end of file \fBlog\fR:

.sp
.in +2
.nf
example% \fB(logname; date; printf "%s\en" "$0 $*") | xargs >>log\fR
.fi
.in -2
.sp

.sp
.LP
The following command invokes \fBdiff\fR with successive pairs of arguments
originally typed as command line arguments (assuming there are no embedded
blank characters in the elements of the original argument list):

.sp
.in +2
.nf
example% \fBprintf "%s\en" "$*" | xargs -n 2 -x diff\fR
.fi
.in -2
.sp

.sp
.LP
The user is asked which files in the current directory are to be archived. The
files are archived into \fBarch\fR \fB;\fR a, one at a time, or b, many at a
time:

.sp
.in +2
.nf
example% \fBls | xargs -p -L 1 ar -r arch
ls | xargs -p -L 1 | xargs ar -r arch\fR
.fi
.in -2
.sp

.sp
.LP
The following executes with successive pairs of arguments originally typed as
command line arguments:

.sp
.in +2
.nf
example% \fBecho $* | xargs -n 2 diff\fR
.fi
.in -2
.sp

.SH ENVIRONMENT VARIABLES
.LP
See \fBenviron\fR(7) for descriptions of the following environment variables
that affect the execution of \fBxargs\fR: \fBLANG\fR, \fBLC_ALL\fR,
\fBLC_COLLATE\fR, \fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
.sp
.ne 2
.na
\fB\fBPATH\fR\fR
.ad
.RS 8n
Determine the location of \fIutility\fR.
.RE

.sp
.LP
Affirmative responses are processed using the extended regular expression
defined for the \fByesexpr\fR keyword in the \fBLC_MESSAGES\fR category of the
user's locale. The locale specified in the \fBLC_COLLATE\fR category defines
the behavior of ranges, equivalence classes, and multi-character collating
elements used in the expression defined for \fByesexpr\fR. The locale specified
in \fBLC_CTYPE\fR determines the locale for interpretation of sequences of
bytes of text data a characters, the behavior of character classes used in the
expression defined for the \fByesexpr\fR. See \fBlocale\fR(7).
.SH EXIT STATUS
.LP
The following exit values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 12n
All invocations of \fIutility\fR returned exit status \fB0\fR.
.RE

.sp
.ne 2
.na
\fB\fB1\(mi125\fR\fR
.ad
.RS 12n
A command line meeting the specified requirements could not be assembled, one
or more of the invocations of \fIutility\fR returned a non-zero exit status, or
some other error occurred.
.RE

.sp
.ne 2
.na
\fB\fB126\fR\fR
.ad
.RS 12n
The utility specified by \fIutility\fR was found but could not be invoked.
.RE

.sp
.ne 2
.na
\fB\fB127\fR\fR
.ad
.RS 12n
The utility specified by \fIutility\fR could not be found.
.RE

.sp
.LP
If a command line meeting the specified requirements cannot be assembled, the
utility cannot be invoked, an invocation of the utility is terminated by a
signal, or an invocation of the utility exits with exit status \fB255\fR, the
\fBxargs\fR utility writes a diagnostic message and exit without processing any
remaining input.
.SH ATTRIBUTES
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
CSI	Enabled
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.LP
.BR echo (1),
.BR shell_builtins (1),
.BR attributes (7),
.BR environ (7),
.BR standards (7)
